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The 12C(p,{\gamma})13N reaction is the onset process of both the CNO and Hot CNO cycles that drive massive star, Red and Asymptotic Giant Branch star and novae nucleosynthesis. The 12C(p,{\gamma})13N rate affects the final abundances of the stable 12,13C nuclides, with ramifications for meteoritic carbon isotopic abundances and the s-process neutron source strength. Here, a new underground measurement of the 12C(p,{\gamma})13N cross-section is reported. The present data, obtained at the Felsenkeller shallow-underground laboratory in Dresden (Germany), encompass the 320-620 keV center of mass energy range to include the wide and poorly constrained E = 422 keV resonance that dominates the rate at high temperatures. This work S-factor results, lower than literature by 25%, are included in a new comprehensive R-matrix fit, and the energy of the 1+ first excited state of 13N is found to be 2369.6(4) keV, with radiative and proton width of 0.49(3) eV and 34.9(2) keV respectively. A new reaction rate, based on present R-matrix fit and extrapolation, is suggested., Comment: Submitted to Phys. Rev. C (Letter)

The 12C(p,γ)13N reaction is the onset process of both the CNO and Hot CNO cycles that drive massive star, Red and Asymptotic Giant Branch star and novae nucleosynthesis. The 12C(p,γ)13N rate affects the final abundances of the stable 12,13C nuclides, with ramifications for meteoritic carbon isotopic abundances and the s-process neutron source strength. Here, a new underground measurement of the 12C(p,γ)13N cross-section is reported. The present data, obtained at the Felsenkeller shallow-underground laboratory in Dresden (Germany), encompass the 320-620 keV center of mass energy range to include the wide and poorly constrained E = 422 keV resonance that dominates the rate at high temperatures. This work S-factor results, lower than literature by 25%, are included in a new comprehensive R-matrix fit, and the energy of the 1 + first excited state of 13N is found to be 2369.6(4) keV, with radiative and proton width of 0.49(3) eV and 34.9(2) keV respectively. A new reaction rate, based on present R-matrix fit and extrapolation, is suggested.

Underground accelerator laboratories are important instruments to measure nuclear reactions with low cross sections in experimental nu- clear astrophysics. The reduced detector background due the shielding from cosmic rays allows the study of astronuclear reactions at energies relevant to Big Bang nucleosynthesis and stellar burning. The reac- tions 3He(a,g)7Be and 12C(p,g)13N have recently been studied at the shallow underground laboratory Felsenkeller Dresden, where a 5 MV accelerator provides several high intensity ion beams and an ultra-low background counting setup for activation measurements. In the talk, the latest scientific results from the Felsenkeller laboratory, its current capabilities and upcoming enhancements will be summarized.

https://u.ganil-spiral2.eu/10.26143/GANIL-2016-E710.html

We measured 135 cross sections of residual nuclei produced in fragmentation reactions of C12, N14, and O13−16,20,22 projectiles impinging on a carbon target at kinetic energies of near 400A MeV, most of them for the first time, with the RB3/LAND setup at the GSI facility in Darmstadt (Germany). The use of this state-of-the-art experimental setup in combination with the inverse kinematics technique gave the full identification in atomic and mass numbers of fragmentation residues with a high precision. The cross sections of these residues were determined with uncertainties below 20% for most of the cases. These data are compared to other previous measurements with stable isotopes and are also used to benchmark different model calculations.

The NeuLAND (New Large-Area Neutron Detector) plastic scintillator based time of flight detector for 0.2-1.6 GeV neutrons is currently under construction at the Facility for Antiproton and Ion Research (FAIR), Darmstadt, Germany. In its final configuration, NeuLAND will consist of 3,000 2.7 m long plastic scintillator bars that are read out on each end by fast timing photomultipliers. Here, data from a comprehensive study of an alternative light readout scheme using silicon photomultipliers (SiPM) are reported. For this purpose, a typical NeuLAND bar was instrumented on each end with a prototype of the same geometry as a 1” photomultiplier tube, including four 6×6 mm2 SiPMs, amplifiers, high voltage supply, and micro- controller. Tests were carried out using the 35 MeV electron beam from the ELBE superconducting linac with its ps-level time jitter in two different modes of operation, namely parasitic mode with one electron per bunch and single-usermode with 1-60 electrons per bunch, using Acqiris fast digitizers. In addition, offline tests using cosmic rays and the NeuLAND data acquisition scheme were carried out. Typical time resolutions of σ≤120 ps were found for ≥ 95% efficiency, improving on previous work at ELBE and exceeding the NeuLAND timing goal of σ be 70-200 s-1, comparable with the unavoidable cosmic-ray induced background. The dataset contains the with the Acqiris Digitzier recorded waveforms and analysis scripts for interpretation of the data. Also GEANT4 simulations of the light propagation in a NeuLAND bar and the electron beam propagation are included.

The dipole strength of the nuclide 76Ge was studied in photon-scattering experiments using bremsstrahlung produced with electron beams of energies of 7.8 and 12.3 MeV at the γELBE facility. We identified 210 levels up to an excitation energy of 9.4 MeV and assigned spin J = 1 to most of them. The quasicontinuum of unresolved transitions was included in the analysis of the spectra and the intensities of branching transitions were estimated on the basis of simulations of statistical γ-ray cascades. The photoabsorption cross section up to the neutron-separation energy was determined and compared with predictions of the statistical reaction model as well as with results of experiments using other reactions.

One of the main neutron sources for the astrophysical s process is the reaction ^{13}C(α,n)^{16}O, taking place in thermally pulsing asymptotic giant branch stars at temperatures around 90 MK. To model the nucleosynthesis during this process the reaction cross section needs to be known in the 150-230 keV energy window (Gamow peak). At these sub-Coulomb energies, cross section direct measurements are severely affected by the low event rate, making us rely on input from indirect methods and extrapolations from higher-energy direct data. This leads to an uncertainty in the cross section at the relevant energies too high to reliably constrain the nuclear physics input to s-process calculations. We present the results from a new deep-underground measurement of ^{13}C(α,n)^{16}O, covering the energy range 230-300 keV, with drastically reduced uncertainties over previous measurements and for the first time providing data directly inside the s-process Gamow peak. Selected stellar models have been computed to estimate the impact of our revised reaction rate. For stars of nearly solar composition, we find sizeable variations of some isotopes, whose production is influenced by the activation of close-by branching points that are sensitive to the neutron density, in particular, the two radioactive nuclei ^{60}Fe and ^{205}Pb, as well as ^{152}Gd.

One of the main neutron sources for the astrophysical s-process is the reaction 13C({\alpha},n)16O, taking place in thermally pulsing Asymptotic Giant Branch stars at temperatures around 90 MK. To model the nucleosynthesis during this process the reaction cross section needs to be known in the 150-230keV energy window (Gamow peak). At these sub-Coulomb energies cross section direct measurements are severely affected by the low event rate, making us rely on input from indirect methods and extrapolations from higher-energy direct data. This leads to an uncertainty in the cross section at the relevant energies too high to reliably constrain the nuclear physics input to s-process calculations. We present the results from a new deep-underground measurement of 13C({\alpha},n)16O, covering the energy range 230-300keV, with drastically reduced uncertainties over previous measurements and for the first time providing data directly inside the s-process Gamow peak. Selected stellar models have been computed to estimate the impact of our revised reaction rate. For stars of nearly solar composition, we find sizeable variations of some isotopes, whose production is influenced by the activation of close-by branching points that are sensitive to the neutron density, in particular the two radioactive nuclei 60Fe and 205Pb, as well as 152Gd, Comment: 7 pages, 4 figures, accepted on PRL on 17th August 2021

The astrophysical Li6(p,γ)Be7 reaction occurs during Big Bang nucleosynthesis and the pre-main sequence and main sequence phases of stellar evolution. The low-energy trend of its cross section remains uncertain, since different measurements have provided conflicting results. A recent experiment reported a resonancelike structure at center-of-mass energy 195 keV, associated to a positive-parity state of Be7. The existence of such resonance is still a matter of debate. We report a new measurement of the Li6(p,γ)Be7 cross section performed at the Laboratory for Underground Nuclear Astrophysics, covering the center-of-mass energy range E=60-350 keV. Our results rule out the existence of low-energy resonances. The astrophysical S-factor varies smoothly with energy, in agreement with theoretical models.

The dipole strength of the nuclide $^{76}$Ge was studied in photon-scattering experiments using bremsstrahlung produced with electron beams of energies of 7.8 and 12.3 MeV at the $\gamma$ELBE facility. We identified 210 levels up to an excitation energy of 9.4 MeV and assigned spin $J$ = 1 to most of them. The quasicontinuum of unresolved transitions was included in the analysis of the spectra and the intensities of branching transitions were estimated on the basis of simulations of statistical $\gamma$-ray cascades. The photoabsorption cross section up to the neutron-separation energy was determined and is compared with predictions of the statistical reaction model. The derived photon strength function is compared with results of experiments using other reactions., Comment: 12 pages, 9 figures

Recent astronomical data have provided the primordial deuterium abundance with percent precision. As a result, Big Bang nucleosynthesis may provide a constraint on the universal baryon to photon ratio that is as precise as, but independent from, analyses of the cosmic microwave background. However, such a constraint requires that the nuclear reaction rates governing the production and destruction of primordial deuterium are sufficiently well known. Here, a new measurement of the $^2$H($p,\gamma$)$^3$He cross section is reported. This nuclear reaction dominates the error on the predicted Big Bang deuterium abundance. A proton beam of 400-1650keV beam energy was incident on solid titanium deuteride targets, and the emitted $\gamma$-rays were detected in two high-purity germanium detectors at angles of 55$^\circ$ and 90$^\circ$, respectively. The deuterium content of the targets has been obtained in situ by the $^2$H($^3$He,$p$)$^4$He reaction and offline using the Elastic Recoil Detection method. The astrophysical S-factor has been determined at center of mass energies between 265 and 1094 keV, addressing the uppermost part of the relevant energy range for Big Bang nucleosynthesis and complementary to ongoing work at lower energies. The new data support a higher S-factor at Big Bang temperatures than previously assumed, reducing the predicted deuterium abundance., Comment: 13 pages, 9 figures, 4 tables; to be published in Phys. Rev. C

Background: Shell hydrogen burning during the asymptotic giant branch (AGB) phase through the oxygen isotopes has been indicated as a key process that is needed to understand the observed 18O/16O relative abundance in presolar grains and in stellar atmospheres. This ratio is strongly influenced by the relative strengths of the reactions 18O(p ,α )15N and 18O(p ,γ )19F in low-mass AGB stars. While the former channel has been the focus of a large number of measurements, the (p ,γ ) reaction path has only recently received some attention and its stellar reaction rate over a wide temperature range rests on only one measurement. Purpose: Our aim is the direct measurement of states in 19F as populated through the reaction 18O(p ,γ )19F to better determine their influence on the astrophysical reaction rate, and more generally to improve the understanding of the nuclear structure of 19F. Method: Branchings and resonance strengths were measured in the proton energy range Eplab=150 -400 keV , using a high-purity germanium detector inside a massive lead shield. The measurement took place in the ultra-low-background environment of the Laboratory for Underground Nuclear Astrophysics (LUNA) experiment at the Gran Sasso National Laboratory, leading to a highly increased sensitivity. Results: The uncertainty of the γ branchings and strengths was improved for all four resonances in the studied energy range; many new transitions were observed in the case of the 334 keV resonance, and individual γ decays of the 215 keV resonance were measured for the first time. In addition a number of transitions to intermediate states that decay through α emission were identified. The strengths of the observed resonances are generally in agreement with literature values. Conclusions: Our measurements substantially confirm previous determinations of the relevant resonance strengths. Therefore the 18O(p ,γ )19F reaction rate does not change with respect to the reaction rate reported in the compilations commonly adopted in the extant computations of red-giant branch and AGB stellar models. Nevertheless, our measurements definitely exclude a nonstandard scenario for the fluorine nucleosynthesis and a nuclear physics solution for the 18O depletion observed in Group 2 oxygen-rich stardust grains.

Recent astronomical data have provided the primordial deuterium abundance with percent precision. As a result, big bang nucleosynthesis may provide a constraint on the universal baryon to photon ratio that is as precise as, but independent from, analyses of the cosmic microwave background. However, such a constraint requires that the nuclear reaction rates governing the production and destruction of primordial deuterium are sufficiently well known. Here, a new measurement of the 2H(p,γ)3He cross-section is reported. This nuclear reaction dominates the error on the predicted big bang deuterium abundance. A proton beam of 400–1650 keV beam energy was incident on solid titanium deuteride targets, and the emitted γ rays were detected in two high-purity germanium detectors at angles of 55∘ and 90∘, respectively. The deuterium content of the targets has been obtained in situ by the 2H(3He,p)4He reaction and offline using the elastic recoil detection method. The astrophysical S factor has been determined at center of mass energies between 265 and 1094 keV, addressing the uppermost part of the relevant energy range for big bang nucleosynthesis and complementary to ongoing work at lower energies. The new data support a higher S factor at big bang temperatures than previously assumed, reducing the predicted deuterium abundance. peerReviewed

The dipole strength of the nuclide 66Zn was studied in photon-scattering experiments using bremsstrahlung produced with electron beams of energies of 7.5 and 13.4 MeV at the γELBE facility as well as using quasi-monoenergetic and linearly polarized photon beams of 30 energies within the range from 4.3 to 9.9 MeV at the HIγS facility. About 140 J = 1 states were identified, out of them 9 with 1+ and 84 with 1- assignments. The quasicontinuum of unresolved transitions was included in the analysis of the spectra and the intensities of branching transitions were estimated on the basis of simulations of statistical γ-ray cascades. As a result, the photoabsorpton cross section up to the neutron-separation energy was determined and compared with predictions of the statistical reaction model. The experimental M1 strengths from resolved 1+ states are compared with results of large-scale shell-model calculations.

Recent astronomical data have provided the primordial deuterium abundance with percent pre- cision. As a result, Big Bang nucleosynthesis may provide a constraint on the universal baryon to photon ratio that is as precise as, but independent from, analyses of the cosmic microwave back- ground. However, such a constraint requires that the nuclear reaction rates governing the production and destruction of primordial deuterium are sufficiently well known. Here, a new measurement of the 2H(p,γ)3He cross section is reported. This nuclear reaction dominates the error on the predicted Big Bang deuterium abundance. A proton beam of 400- 1650keV beam energy was incident on solid titanium deuteride targets, and the emitted γ-rays were detected in two high-purity germanium detectors at angles of 55◦ and 90◦, respectively. The deuterium content of the targets has been obtained in situ by the 2H(3He,p)4He reaction and offline using the Elastic Recoil Detection method. The astrophysical S-factor has been determined at center of mass energies between 265 and 1094 keV, addressing the uppermost part of the relevant energy range for Big Bang nucleosynthesis and complementary to ongoing work at lower energies. The new data support a higher S-factor at Big Bang temperatures than previously assumed, reducing the predicted deuterium abundance.

One of the main neutron sources for the astrophysical s process is the reaction C 13 (α ,n )O 16 , taking place in thermally pulsing asymptotic giant branch stars at temperatures around 90 MK. To model the nucleosynthesis during this process the reaction cross section needs to be known in the 150-230 keV energy window (Gamow peak). At these sub-Coulomb energies, cross section direct measurements are severely affected by the low event rate, making us rely on input from indirect methods and extrapolations from higher-energy direct data. This leads to an uncertainty in the cross section at the relevant energies too high to reliably constrain the nuclear physics input to s -process calculations. We present the results from a new deep-underground measurement of C 13 (α ,n )O 16 , covering the energy range 230-300 keV, with drastically reduced uncertainties over previous measurements and for the first time providing data directly inside the s -process Gamow peak. Selected stellar models have been computed to estimate the impact of our revised reaction rate. For stars of nearly solar composition, we find sizeable variations of some isotopes, whose production is influenced by the activation of close-by branching points that are sensitive to the neutron density, in particular, the two radioactive nuclei Fe 60 and Pb 205 , as well as Gd 152 .

Statusreport SiPM readout for NeuLAND (saturation effects, dark rate and time resolution measurements)

The dipole strength of the nuclide Zn66 was studied in photon-scattering experiments using bremsstrahlung produced with electron beams of energies of 7.5 and 13.4 MeV at the γELBE facility as well as using quasimonoenergetic and linearly polarized photon beams of 30 energies within the range of 4.3 to 9.9 MeV at the HIγS facility. A total of 128 J=1 states were identified, among them 9 with 1+ and 86 with 1- assignments. The quasicontinuum of unresolved transitions was included in the analysis of the spectra and the intensities of branching transitions were estimated on the basis of simulations of statistical γ-ray cascades. As a result, the photoabsorption cross section up to the neutron-separation energy was determined and compared with predictions of the statistical reaction model. The experimental M1 strengths from resolved 1+ states are compared with results of large-scale shell-model calculations.